1. Field of the Invention
The present invention relates to orthopaedic fixation devices, and more particularly to an improved dynamic wrist fixator module that uses a flexible coupler for connecting two external fixation rods. The module also contains a movable clip to restrain the motion of the coupler. The apparatus can be used to hold pin clamps which support bone pins for attachment to the bone parts.
2. General Background of the Invention
One of the preferred methods of treating bone fractures such as distal radius fractures is to reduce the fracture by distracting the surrounding ligaments with an external fixation device. This technique is known as ligamentotaxis. With this method, the wrist is immobilized for six to eight weeks until healing is complete.
One problem with leaving the wrist immobilized for long periods of time is the possibility of wrist stiffness or cartilage deterioration due to poor joint nutrition. A joint relies on movement to allow the fluids to bathe the cartilage and provide a proper environment for the joint.
Some of the existing external fixators address this issue by providing some joint motion. However, the existing designs constrain the fixator to certain axes of rotation which must be properly aligned with the anatomical axis of wrist or joint motion. Since it is very difficult to align the fixator with the exact axis of joint movement, there is often a mismatch between the fixator axis and the joint axis which can result in the displacement of the bone fragment and loss of fracture reduction. This displacement results from the wrist being forced to move about the axis of the fixator which goes against its normal movement.
An example of a technique of multi-planar ligamentotaxis is described by Dr. John Agee in an article published in Orthopaedic Clinics Of North America, Vol. 24, No. 2, April 1993 and entitled "External Fixation: Technical Advances Based Upon Multi-Planar Ligamentotaxis". John Agee is also the named patentee of the U.S. Pat. Nos. 4,548,199; 4,611,586; and 4,922,856. The fixator developed by Dr. Agee provides a method of achieving multi-planar ligamentotaxis through gradual turning of worm screws.
Several fixation systems have been patented that relate to the bone segments. An example is U.S. Pat. No. 4,483,334, issued to William Murray and entitled "External Fixation Device". The '334 patent discloses a device for holding bone segments in known relation to each other. The apparatus includes a pair of bone clamp assemblies each secured to bone pins extending from the bone segments. A bridge extends between the pin clamp assemblies and a specialized high friction universal assembly connects the bridge to each of the pin clamp assemblies.
U.S. Pat. No. 5,207,676, issued to Jose Canadell et al., relates to an external fixator with controllable damping. This external fixator disclosed in the '676 patent is for the correction and reduction of bone fragments. The apparatus comprises a bar fastened to a biocompression system on which the bar and system are disposed upon supports for fastening pins inserted into bones.
A spinal fixator reduction frame is the subject of U.S. Pat. No. 5,219,349. A reduction frame disclosed in the '349 patent is secured to shaft handles extending from the pedicle screws of a Vermont Spinal Fixator type implant. Shaft clamps secure two T-handles of the reduction frame to the shaft handles. A lower-rod assembly joins the two opposite T-frames by means of lower-rod clamps. The shaft clamps are provided with four degrees of freedom. The joint between the lower-rod assembly and T-handle is provided with five degrees of freedom. The lower-rod assembly and the T-handle are provided with power screw threads to allow for precise translational control. The shaft clamps and lower-rod clamps are provided with taper fit joints to allow for infinite rotational adjustment and fixture. An upper-rod assembly is also provided on the T-handles to produce rotation of the T-handles by providing means for changing the distance between the upper ends of the T-handles. Finger grips are provided on the upper-rod assembly to allow the surgeon to easily use one hand to either apply or monitor the force acting along the upper-rod.
The Hardy U.S. Pat. No. 5,429,637, discloses an external modular fixator for immobilization of a fracture. The apparatus includes elements functioning as clamps and receiving anchor pins to be fixed in a predetermined angular position on either side of a fracture. A mobilization relay body is configured to be attached to the fracture. The mobilization body has a device for locking which is used to lock the clamps. A fixator and the mobilization relay bodies are lockable in various chosen arrangements. The device is shown affixed to a patient's lower arm and wrist area.
The Pennig U.S. Pat. No. 5,443,465 refers to an osteosynthesis aid which is used in particular for the fixation of a pelvis and includes a central body which is formed of at least two arm or link members, each of which has an elongated slot through which a lock bolt is passed to provide a releasable clamped joint and each of which also has releasably secured ball-joint connection to an end-connecting clamp for bone-pin or bone-screw anchorage to an afflicted bone.
A Russian Patent SU 1491-492-A1 discloses a femur neck fracture osteosynthesis device that has a support in the form of plates with inclined slots for pins. The plates have apertures for pin locks. The pin locks are designed in the form of threaded rods with nuts and washers. The plates are in parallel plane with an offset greater than the sum of the thickness of the plates and the pin diameter. The plates are interconnected by connecting pieces. Pins are passed after passing through the aiming pin and are locked by the pin locks. This device has an advantage of simplifying the design by allowing crossing-over angle in the planes parallel with the femur axis.